Platform Topside for an Offshore Platform and Method for Installing Such a Platform Topside

ABSTRACT

A platform topside for an offshore platform including a self-floating superstructure with a stable floating position, projections on the superstructure, means for mounting legs in an upright arrangement in the projections, wherein the projections and the means for mounting legs are arranged above the water line or not far below the water line, means for displacing the legs in the longitudinal direction of the legs in the means for mounting and means for fixing the legs in their positions in the means for mounting.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable

BACKGROUND OF THE INVENTION

The invention relates to a platform topside for an offshore platform and to a method for installing a platform topside for an offshore platform.

Offshore platforms are artificial platforms in the ocean, which mostly serve to house technology and accommodations for personnel. The invention relates in particular to offshore platforms for collecting electrical energy from offshore wind turbines and its transfer to an onshore station in the rectified or unrectified state. Such offshore platforms are also called transformer platforms. The invention is also applicable to other offshore areas.

Offshore platforms with a substructure made of a tubular steel frame are already known. The tubular steel frame is towed to the setup site on a barge using a tugboat. There, it is lowered to the ocean floor by means of floating cranes. Furthermore, piles are inserted into the corresponding bearings of the substructure using floating cranes and driven into the ocean floor. The piles are grouted with the substructure.

Furthermore, a platform topside is transported to the setup site on a barge and legs are inserted in the corresponding bearings of the platform topside by means of floating cranes. The legs are inserted in the upper openings of the piles with their lower ends near the ocean floor and grouted with them. The underwater work must be inspected and executed by dive robots or divers.

The use of self-floating platform topsides that are towed to the setup site with inserted legs is also already known. There, the legs are connected with the piles in the described manner.

BRIEF SUMMARY OF THE INVENTION

The installation of the known offshore platforms is complex.

Based on this, the object of the invention is to provide a platform topside for an offshore platform and a method suitable for installing a platform topside for an offshore platform, which reduces the effort for the erection of the offshore platform.

The platform topside for an offshore platform according to the invention includes:

-   -   a self-floating, superstructure with stable floating position,     -   projections on the superstructure,     -   means for mounting legs in an upright arrangement in the         projections,     -   wherein the projections and the means for mounting legs are         arranged above the water line or not far below the water line,     -   means for displacing the legs in the longitudinal direction of         the legs in the means for mounting and     -   means for fixing the legs in their positions in the means for         mounting.

The platform topside according to the invention comprises a self-floating, superstructure with a stable floating position, which is preferably made in shipbuilding design from plates and profiles. The superstructure can be brought from the shore to the setup site at sea in a self-floating manner. Tugboats can be used for this. It is not required to provide the superstructure with an own drive. The use of barges and other transport means for the transport of the platform topside to the setup site is not needed. Preferably, the width of the water line of the superstructure is designed such that taking on ballast water for the transit can be foregone. At the setup site, the platform topside can be installed on any substructure, which has connection points or respectively interfaces for a platform topside to be installed above the surface of the water or not far below the surface of the water. For this, the means for mounting legs are arranged in projections of the platform topside and the projections as well as the means for mounting are arranged above the water line or not far below the water line. The cross-section of the superstructure is designed such that it lies in the area of the means for mounting the legs above the water line or not far below the water line. It is hereby achieved that the connection between the platform topside and the substructure can be performed above the surface of the water or not far below the surface of the water and thus within the visual range. For this, the platform topside with the projections is placeable above the connection points of the substructure and the legs can then be lowered to the connection points. For this, the means for the displacing of the legs are used, which make it possible to displace the legs in their longitudinal direction. The connection of the legs of the platform topside with the substructure can take place within visual range and under particularly beneficial conditions. Dive robots or divers are not required for this. The work can be done from the platform topside or from work rafts positioned next to the projections. The use of ship cranes for unloading the platform topside from a barge and placing the platform topside below the substructure and the insertion and lowering of the legs can be omitted. The superstructure has a stable floating position, i.e. it automatically erects itself from the laterally inclined position as long as the incline does not exceed a maximum value. As a result, the platform can be brought into a defined initial position, from which the legs can be easily lowered to the connection points of the substructure. The substructure can be used as an aid for the positioning of the platform topside. The means for displacing the legs are used in order to lift the platform topside to an installation height after the connection of the legs with the interfaces of the substructure. This height is dimensioned such that the water level does not reach the platform topside and the highest expected wave passes below the platform topside. In this position, the legs are fixed by means of the means for fixing.

The connection points of the substructure preferably protrude from the surface of the water by a maximum of 6 meters, more preferably by a maximum of 3 meters, most preferably by a maximum of 1.5 meters.

Connection points arranged below the surface of the water are preferably arranged within visual range below the surface of the water. The visual range is the area below the water line that can be seen by an adult person with normal vision with the unaided eye. In the case of an interface below the water line, the visual range can be extended by suitable measures.

This takes place through elements attached to the substructure that are visible above the water line and determine the position of the interface. The design can be realized e.g. with markings in the form of rods or tubes, which are lead up from the substructure to above the water line and determine the position of the interface.

The connection points arranged below the water line preferably have a maximum distance of 6 meters from the surface of the water, more preferably a maximum of 3 meters from the surface of the water, most preferably a maximum of 1.5 meters from the surface of the water.

The dimensioning of the substructure and the platform topside is based on a certain water level according to a water level analysis. This is preferably the MWL (mean water level) or LAT (lowest astronomical tide) or HAT (highest astronomical tide), or another defined water level from tidology. Depending on the time window needed for the connection of the substructure and the platform topside, a suitable water level can be selected, on which the dimensioning of the substructure and the platform topside is based. The water level analysis provides the respective water levels for specified installation times.

The means for mounting the legs in the upright arrangement or respectively upright position are designed such that they mount the legs in the most vertical alignment possible. The means for mounting the legs preferably mount the legs in the vertical alignment, if applicable with deviations (maximum 5°, preferably maximum 2°).

In accordance with an advantageous embodiment of the invention, the legs are mounted in the means for mounting and the platform topside equipped with the legs is self-floating with a stable floating position. The legs are thereby fixed in their position in the means for displacing by means of the means for fixing. In this embodiment, the superstructure serves as a transport means for the legs, in order to float the superstructure together with the legs to the setup site. The legs do not need to be transported separately to the setup site at sea.

The means for fixing the legs serve to fix the legs in a raised initial position during transit from the shore to the setup site at sea. Furthermore, they serve to fix the legs in the lowered position if the legs are connected with the connection points of the substructure.

According to a preferred embodiment, the structure has projections on both sides of a center part and/or two side parts with projections in the form of a bridge. The first variant has the advantage that the connection points of the legs with the substructure are visible and accessible from locations next to the superstructure. Moreover, the legs are located on the outer edge of the platform topside, which is advantageous for the statics of the offshore platform. In the case of the second variant, the superstructure is designed in its cross-section like a catamaran, and the two projections are combined into a single bridge between the two side parts. The third variant is a combination with a center part and side parts on both sides of the center part as well as projections in the form of bridges connecting the center part and the side parts. The third variant has a cross-section like a trimaran. In the case of the first variant, the center part contains one or more buoyancy cells and, in the case of the second variant, the side parts. In the case of the third variant, the side parts and the center part can contain buoyancy cells. The second variant has a more stable floating position than the first.

In the case of a further embodiment, the means for mounting legs each have an upper leg bearing and a lower leg bearing arranged at a distance from it for mounting a leg. Stable means for mounting legs in vertical alignment are hereby achieved with relatively little structural effort.

According to another embodiment, the upper leg bearings are integrated into the main deck of the superstructure and the lower leg bearings into a bottom wall of the projections. This design is constructive and especially beneficial from a production point of view.

According to another embodiment, the means for displacing in the vertical direction are simultaneously the means for fixing the legs in vertical positions. Construction effort is hereby saved. For example, known jacking systems designed as bolts in a pin-in-hole system or a strand jacking system can be used as combined means for displacing and fixing the legs. These systems can be partially retrofitted and used for other purposes after the installation of the platform topside. This applies in particular to hydraulic and other lifting components.

According to another embodiment, the legs have a cone tapering downward on the bottom end and/or a ledge at a distance from the bottom end. The cone serves as an insertion aid during the connection of the legs with the substructure. The cone is preferably connected with a pile or a connection unit installed on the pile. The pile or respectively the connection unit is hollow-cylindrical and the cone is easily insertable into an upper opening of the pile or respectively of the connection units. Once the legs are completely inserted into the pile or the connection unit, the ledge is supported on the upper edge of the piles or the connection unit.

The method according to the invention suitable for installing a platform topside comprises the following steps:

-   -   constructing the platform,     -   bringing the platform to the setup site in a self-floating         manner,     -   positioning the platform above a substructure,     -   lowering the legs of the platform and connecting them with the         substructure above the surface of the water or not far below the         surface of the water,     -   raising the platform topside by means of the legs and     -   fastening the platform on the legs.

According to one embodiment of the method, the platform topside is equipped with the legs before being brought to the setup site.

According to another embodiment of the method, the legs are connected with piles or towers of a substructure above the surface of the water or not far below the surface of the water.

According to another embodiment, the legs are connected in a form-fit manner with the piles or towers of a substructure.

According to another embodiment, the substructure is used as a positioning aid of the platform topside during the positioning of the platform topside above the substructure.

According to another embodiment, the means for displacing the legs are at least partially dismantled from the platform topside for other uses after the lowering of the legs and the later raising of the platform topside.

According to another embodiment, a cable tower on the substructure is connected with the platform topside after the raising of the platform topside.

In this patent application, the terms “above” and “below” refer to the arrangement of the offshore platform with the substructure below the platform topside with upright piles and vertically upright legs.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is explained in greater detail below based on the included drawings of an exemplary embodiment.

In the drawings:

FIG. 1 shows an offshore platform consisting of a substructure and a platform topside in a perspective view diagonally from above and from the side;

FIG. 2 shows a substructure of the offshore platform with lowered piles in a perspective view diagonally from above and from the side;

FIG. 3 shows the substructure in the same state in a side view;

FIG. 4 shows the substructure in a top view;

FIG. 5 shows a tower of the substructure with an inserted pile in a horizontal section;

FIG. 6 shows the tower with the inserted pile in a vertical section;

FIG. 7 shows a bottom bearing of the tower with the inserted pile in a vertical section;

FIG. 8 shows a clamping device of the tower with the inserted pile in a vertical section;

FIG. 9 shows the substructure with piles in the raised initial position in the floating state in a vertical section;

FIG. 10 shows the lowered substructure with piles driven into the ocean floor in a vertical section;

FIG. 11 shows the platform topside in a raised state on the legs in a perspective view diagonally from above and from the side;

FIG. 12 shows the platform topside in the same position on the legs in a side view;

FIG. 13 shows the platform topside with the legs in the raised initial position in the floating position in a vertical section;

FIG. 14 shows a jacking system for displacing the legs with respect to the platform topside in a certain position of the leg in a side view;

FIG. 15 shows the same jacking system in a lower position of the leg with respect to FIG. 10 in a side view;

FIG. 16 shows an interface between a pile and a leg before the establishment of the connection in a side view;

FIG. 17 shows the same interface after the establishment of the connection in a side view;

FIG. 18 shows the same interface after the establishment of the connection in a vertical section;

FIG. 19 shows the same platform topside during connection of the legs with the piles of the substructure in a vertical section;

FIG. 20 shows the offshore platform after the raising of the platform topside with respect to the legs in a vertical section.

DETAILED DESCRIPTION OF THE INVENTION

While this invention may be embodied in many different forms, there are described in detail herein a specific preferred embodiment of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiment illustrated.

According to FIGS. 1 and 20, an offshore platform 1 comprises a substructure 2, which is deposited on the ocean floor 3. The substructure 2 forms with piles 4 the foundation structure of the offshore platform 1. The piles 4, also called “nails”, are driven into the ocean floor 3, in order to establish a pile foundation and to anchor the substructure 2 on the ocean floor 3. The piles 4 serve to transfer loads from the platform topside 5. The piles 4 are preferably circular-cylindrical. They are preferably hollow-cylindrical.

The platform topside 5 is a supporting structure, which is arranged in the area above the surface of the water 6 and outside the sphere of influence of the sea.

The platform topside 5 is supported on the foundation structure via legs 7. The legs 7 are each incorporated on the top into the structure of the platform topside 5 and connected on the bottom with a pile 4. The legs 7 are preferably circular-cylindrical. They are preferably hollow-cylindrical.

According to FIG. 2 through 4, the substructure 2 has a structure 8, which comprises a horizontal, rectangular base frame 9. The base frame 9 has four straight-line frame parts 10.

Four towers 11 protrude upwards from frame 9. On the bottom, the towers 11 are flush with the bottom side of the base frame 9. The towers 11 are hollow bodies. In the example, they have an octagonal cross-section. Each tower 11 is located on one corner of the base frame 9 and simultaneously forms a connection element between two neighboring frame parts 10. On the top, each of the frame parts 10 carry support elements 12 on the ends, which support the towers 11 laterally.

On the bottom end, each of the hollow-cylindrical towers 11 have a circular, bottom opening 13 and, on the top end, a circular, upper opening 14 for the passage of a pile 4.

According to FIGS. 5 and 6, each tower 11 comprises a sleeve-like, bottom bearing 15 connecting to the bottom opening 13 and a sleeve-like, upper bearing 16 connecting to the upper opening 14. A pressure seal 17 for sealing the bottom bearing 16 from the pile 4 is present in the bottom bearing 15.

The bottom structure 8 made up of the base frame 9 and the towers 11 is a shipbuilding steel construction made of plates and profiles. The plates and profiles are welded together.

There are several separate tanks 18 located inside the bottom structure 8. In the example, a separate tank 18 is arranged in each frame part 8. The tanks 18 are each connected with means for flooding 19 and means for pumping out 20, via which each tank can be flooded and pumped out separately. The means for flooding 19 are suitable valves. The means for pumping out 20 are removable pumps with associated lines.

According to FIGS. 5 and 6, a hollow area sealed laterally and on the bottom is present in each tower 11 around the pile 4 when the pile 4 is held in the lower and upper bearing 15, 16. The hollow area forms another tank 21. This is in turn separately floodable and pumpable via other separate means for flooding 22 in the form of valves and other means for pumping out 23 in the form of pumps and associated lines.

Furthermore, according to FIGS. 6 and 8, means for the fixation and braking 24 of a pile 4 in a vertical position is present in each tower. The device that holds the piles in position in a force-fit or form-fit manner can hereby be mechanical or hydraulic. According to FIG. 8, they are clamping jaws 25, 26, which rest on a horizontal bearing 27 and enclose a pile 4 on different sides. Through the tightening of the clamping jaws 25, 26, the pile 4 is fixable so that it is not displaced downwards with respect to the tower due to its own weight. The piles 4 can be drained in a controlled manner by releasing the brake device.

The tanks 18, 21 are dimensioned such that they ensure the buoyancy for the floating of the substructure 2 including the piles 4 in the empty state. The substructure 2 is self-floating and has a stable floating position. It does not have its own drive.

According to FIG. 2, a control stand 28 is present on the top of at least one tower 11. The means for flooding 19 are connected with means for controlling 29 the means for flooding in the control stand 28.

Furthermore, measurement and display devices 30, 31 for capturing and displaying the trim of the structure 8 are present in the control stand.

Moreover, the substructure comprises a vertical cable tower 32, which is made of a bundle of individual pipes 33. The cable tower 32 is arranged outside of the frame 9. It is connected with a tower 11 laterally via braces 34.

In order to compensate for the weight of the cable tower 32, the base frame 9 in the neighboring corner is provided with a prismatic buoyancy body 35. The buoyancy body 35 stabilizes the base frame 9 at the same time.

The height of the towers 11 is adjusted to the water level at the setup site so that the upper ends of the towers 11 protrude out of the water at the time of the installation of the offshore platform 1.

In one example, the length of the frame is 47.5 meters and its width on the main deck is 41.5 meters. The substructure is intended for a setup site with a lowest astronomical tide (LAT) of 24 meters. The height of the towers 11 is 25.5 meters so that the towers 11 at the setup site protrude out of the water at certain times under normal sea states, for example in the case of moderate swell conditions (sea state 4).

The cable tower 32 is measured such that it protrudes up to the platform topside 5. In the example, its length is 40 meters.

The piles 4 are hollow and cylindrical. On the bottom, they are preferably closed during the transport and are opened on the bottom for driving. According to FIG. 16 through 18, the piles 4 have an opening 35 on the top, into which a leg 5 can be inserted.

The substructure 2 is produced in a construction dock of a shipyard.

During the construction phase, the equipment including the means for flooding and pumping out (19, 20, 21, 22) and optionally the piles 4 are installed in the substructure 2. The piles 4 can be inserted into the lower and upper bearings 15, 16 of the towers 11 in the construction dock by means of a (portal) crane and fixed therein in an initial position by means of the clamping jaws 25, 26, in which they do not protrude on the bottom from the base frame 9.

Optionally, the cable tower 32 can be installed in the construction dock.

After complete assembly of all components, the substructure 2 is floated in the construction dock and moved to the finishing pier for final finishing and testing. After structural approval, the transit of the substructure 2 to the installation site takes place in the towing convoy with corresponding temporary firing. The floating state is shown in FIG. 9.

If necessary, the ocean floor 3 is prepared before installing the substructure 2, if its irregularities are too significant. For this, an even surface is created on the ocean floor 3, which meets the defined tolerances for the installation of the offshore platform 2 and a suitable subsurface for the substructure 2 is formed.

The substructure 2 is positioned above the setup site by sea-going tugboats. At the setup site, the tugboats can automatically be held in a predetermined position by means of a dynamic positioning system. The DP2 system can be used, for example.

The flooding of the tanks 18, 21 takes place manually via the control stand 28 of the substructure depending on the trim displayed by the display device 31.

If necessary, the tanks 18, 21 can be flooded using a remote control. The trim is monitored by the measurement devices 30 on the substructure 2 and, if necessary, the measurement results are transferred to a location outside the substructure 2, from which the flooding can be controlled remotely.

Once the substructure 2 is resting on the ocean floor, the piles 4 are lowered using gravity. For this, the clamping jaws 25, 26 are controlled from the control stand 28. If necessary, the lowering of the piles 4 is braked by means of the clamping jaws 25, 26. Under their own weight, the piles 4 are only partially driven into the ocean substrate 3. They are additionally driven into the ocean substrate 3 with pile hammers, which are positioned on the top of the piles.

The mounting of the piles 4 in the towers 11 serves to guide the piles 4 during the driving process. The piles 4 are driven into the ocean substrate 3 until their top end is flush with the top end of the towers 11. This is shown in FIG. 10.

The piles 4 are then connected in a form-fit manner with the substructure 2. The form-fit connection preferably takes place through grouting. For this, liquid concrete or artificial resin or another hardening, groutable mass is injected into a gap 36 between the pile 4 and the lower bearing 16. Preferably, the lower bearing 15 is also provided with an upper seal 37, which, together with the pressure seal 17, prevents the grouting medium 38 from escaping out of the gap 36. Through the grouting, the tower 11 is also permanently sealed on the bottom.

The upper openings 35 of the piles 4 are thus located as interfaces for receiving the legs 7 for carrying the platform topside 5 at the time of installation above the surface of the water 6.

According to FIGS. 11 and 12, the platform topside 5 has a superstructure 39, which has a box-shaped center part 40 and projections 42, 43 above the water line 41, i.e. above the floating water line of the platform topside 5. The side walls 44, 45 of the superstructure 39 are thus inserted below the projections 42, 43. The structure 39 thus has a symmetrical T-shaped cross-section (see FIG. 12), wherein the center part 40 forms the vertical T-post and the projections 42, 43 form the laterally protruding beam parts of the horizontal T-beam.

According to FIG. 13, the center part 40 is partitioned off from the projections 42, 43. It has a double floor 46 on the bottom and it is closed by a main deck 47 on the top. It has one or more buoyancy cells 48, which are separated from each other by transverse bulkheads.

Means for mounting 49 the legs 7 are located in the lateral projections 42, 43. For each leg 7, there is a lower leg bearing 50 and an upper leg bearing 51, which align with each other. The lower leg bearing 50 is arranged in a bottom wall 52 of the projection 42, 43 and the upper leg bearing 51 is arranged in a cover wall 53 of the projection 42, 43, which is a lateral strip of the main deck 47 of the platform topside 5. The bottom wall 52 and the cover wall 53 of the projections 42, 43 have reinforcements on the lower and upper leg bearings 50, 51. The lower and upper leg bearings 50, 51 are circular through holes through the bottom wall 52 and the cover wall 53 at the reinforced positions.

The superstructure 39 is also mainly symmetrical in the longitudinal direction.

Personnel rooms or respectively service rooms can be located in the superstructure 39.

A jacking system 54, which is shown separately in FIGS. 14 and 15, is present above each upper leg bearing 51. The jacking system 54 has a fixed rest 55 permanently fixed on deck. This is hereby a plate with a vertical through hole 56, through which a leg 7 can be inserted. Furthermore, the fixed rest 55 has a horizontal hole 57, which extends from an outside of the fixed rest 55 up to the inner circumference of the vertical through hole 56.

According to FIGS. 14 and 15, the jacking system 54 comprises a displaceable rest 58. This is hereby also a plate with a vertical through hole 59, which receives a leg 7. Furthermore, the fixed rest 55 has a horizontal hole 60, which extends from an outside of the displaceable rest 58 up to the inner circumference of the vertical through hole 59.

Furthermore, the jacking system 54 has hydraulic cylinders 61, which are fixed on the bottom on the fixed rest 55 and on the top on the displaceable rest 58. The displaceable rest 58 is vertically liftable or respectively lowerable by means of the hydraulic cylinder 61. It goes without saying that the hydraulic cylinders 61 include a hydraulic controller and a pressurized supply with a hydraulic medium.

The legs 7 are each provided with a series of horizontal blind holes 62. When the jacking system 53 is not in operation, the leg 7 is locked to the platform topside 5 by inserting a bolt 63 into the horizontal hole 57 of the fixed rest 55 and into a horizontal blind hole 62 of the leg 7 so that it is not displaceable in the axial direction.

The jacking system 54 is a pin in hole system. Alternatively, a strand jacking system can be provided.

The buoyancy cells 48 are measured such that the superstructure 39 is self-floating when the legs 7 are mounted in the means for mounting 49 the legs and fixed by means of the jacking systems 54. The water line 41 is thereby located below the projections 42, 43.

Furthermore, the platform topside 5 is designed such that it has a stable floating position when the legs 7 are inserted into the lower and upper leg bearings 50, 51 and do not protrude beyond the projections 42, 43 on the bottom. Preferably, the width of the water line 41 of the superstructure 39 is designed such that the taking on of ballast during the floating of the superstructure 39 can be foregone.

The weight distribution of the platform topside 5 is approximately homogeneous. It is thus not necessary to use trim tanks to hold the platform topside 5 in a stable trim. But trim tanks can be used, if needed.

The platform topside 5 is self-floating and does not have its own drive. Thus, transport on a barge is not necessary.

For example, the platform topside has a length of 73 m, a width on the main deck of 49.5 m, on the bottom a width of 31.5 m and a height from the lower edge to the deck of 26.5 m.

According to FIG. 16 through 17, the diameter of the legs 7 at a short distance from their lower ends exceeds the inner diameter of the upper opening 35 of the piles 4. There, each of the legs 7 has a ledge 64, under which its outer diameter is smaller than the inner diameter of the piles 4 by a certain amount. On the bottom, the legs 7 have a frustoconical section 65.

With the frustoconical section 65, the leg 7 is insertable into the upper opening 35 of a pile 4, until the ledge 64 rests on the upper edge of the pile 4. A hollow-cylindrical gap 65 remains between the section with the reduced diameter of the leg and the pile.

In the example, the length of the legs 7 is approximately 45 m.

The platform topside 5 can be built in a construction dock of a shipyard.

During the construction phase, the legs 7 are preferably inserted into the lower and upper leg bearings 50, 51 by means of a (portal) crane and secured in the lower rest 55 by means of bolts 63.

For the floating of the platform topside 5, at least a temporary seal of the platform topside 5 is ensured.

The platform topside 5 is then floated at the setup site and hauled to the shipyard pier for final rig up and for testing. The installation of the removable components of the jacking system 54 can then take place on the main deck 47.

The platform topside 5 is then floated to the installation site in the towing convoy with corresponding temporary firing.

At the installation site, the platform topside 5 is floated into position above the substructure 2 and positioned on the substructure 2 with the help of tugboats at the defined point in time by positioners or respectively fenders in accordance with water level analysis. The substructure 2 can hereby be used as an insertion and positioning aid.

The legs 7 are then located in the projections 42, 43 exactly above the assigned piles 4 of the substructure 2.

The legs 7 are then lowered onto the piles 4 by means of the jacking systems 54 so that the legs 7 engage with the lower ends into the upper openings 35 of the piles 4 and fit with the ledges 64. The lowering takes place by means of the jacking systems 54 such that the hydraulic cylinders 61 are moved apart and the horizontal hole 60 of the displaceable rest 58 is aligned with a blind hole 62 of a leg 7. A bolt 63 is then inserted into the horizontal hole 60 and the blind hole 62 and the bolt 63 is pulled out of the fixed rest 55.

The hydraulic cylinders 61 are then moved together whereby the legs 7 are lowered. They were lowered until a blind hole 62 of the leg 7 is aligned with the horizontal hole 57 of the fixed rest 55. Each of the legs 7 is then secured by means of a bolt, which is inserted into the horizontal hole 57 of the fixed rest 55 and the blind hole 62 of the leg 7. The bolt 63 is then pulled out of the displaceable rest 58 and the processes described above are repeated until the legs 7 are in their final position.

When the legs 7 engage in the piles 4 according to FIG. 18, they are connected in a form-fit manner with the piles. For this, they are preferably grouted with the piles in that a grouting agent 67 is inserted into the gap 66.

The above work is comparatively easy to perform since the interface or respectively connection point between the legs 7 and the piles 4 is located above the water surface 6 or not far below the surface of the water 6.

After the establishment of a permanent connection between the legs 7 of the platform topside 5 and the piles 4 of the substructure 2, the platform topside 5 is raised to the predetermined installation height. The installation height is selected such that the highest possible wave (“century wave”) to be expected according to the water level analysis still passes below the platform topside. In the example, the installation height is 161 m above LAT.

The raising of the platform topside 5 is performed by means of the jacking systems 54. They are operated in the manner described above, wherein the platform topside 5 is raised by pulling the hydraulic cylinders 61 together. Once the platform topside 5 has reached the installation height, the legs 7 secured in the end position by inserting bolts 63 into the horizontal hole 57 of the fixed rest 55 and in blind holes 62 of the legs 7. An elastically mounted bolt connection can be used for this.

The finished offshore platform 1 is shown in FIG. 1. The cable tower 32 reaches up to a lateral projection 42. There, a bridge 68 is additionally attached, via which sea cables can be guided into the platform topside 5 and the installation work is facilitated.

The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims.

Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim 1 should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below.

This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto. 

What is claimed is:
 1. A platform topside for an offshore platform comprising a self-floating superstructure with a stable floating position, projections on the superstructure, means for mounting legs in an upright arrangement in the projections, wherein the projections and the means for mounting legs are arranged above the water line or not far below the water line, means for displacing the legs in the longitudinal direction of the legs in the means for mounting and means for fixing the legs in their positions in the means for mounting.
 2. The platform topside according to claim 1, in which the legs are mounted in the means for mounting the legs and the superstructure equipped with the legs is self-floating with a stable floating position.
 3. The platform topside according to claim 1, in which the superstructure has projections on both sides of a center part or in which the structure has two side parts with these connecting projections in the form of a bridge.
 4. The platform topside according to claim 1, in which the means for mounting legs each have an upper leg bearing and a lower leg bearing arranged at a distance from it for mounting a leg.
 5. The platform topside according to claim 4, in which the upper leg bearings are integrated into the main deck of the superstructure and the lower leg bearings are integrated into a bottom wall of the projections.
 6. The platform topside according to claim 1, in which the means for displacing the legs are simultaneously the means for fixing the legs.
 7. The platform topside according to claim 1, in which the legs have on the bottom end a downward tapering cone and/or a ledge at a distance from the bottom end.
 8. A method suitable for installing a platform topside of an offshore platform according to claim 1, in which the platform topside is constructed, the platform topside is brought to the setup site in a self-floating manner, the platform topside is positioned above a substructure, the legs of the platform topside are lowered and connected with the substructure above the surface of the water or not far below the surface of the water, the platform topside is raised with respect to the legs and the platform topside is fastened on the legs.
 9. The method according to claim 8, in which the platform topside is equipped with the legs before being brought to the setup site.
 10. The method according to claim 8, in which the legs are connected with piles or towers of a substructure above the surface of the water or not far below the surface of the water.
 11. The method according to claim 8, in which the legs are connected in a form-fit manner with the towers and/or piles of a substructure.
 12. The method according to claim 8, in which the substructure is used as a positioning aid for the platform topside during the positioning of the platform topside above the substructure.
 13. The method according to claim 8, in which the means for displacing are at least partially dismantled from the offshore platform for other uses after the lowering of the legs and subsequent raising of the platform topside.
 14. The method according to claim 8, in which a cable tower on the substructure is connected with the platform topside after the raising of the platform topside.
 15. The method according to claim 8, in which the legs are connected with the substructure at a maximum of 6 meters, preferably 3 meters, more preferably 1.5 meters above or below the surface of the water. 